Photosensitive resin composition and circuit formation substrate using the same

ABSTRACT

A photosensitive resin composition for an interlayer insulating film or a protective film of a substrate for circuit formation, which includes a polymer (a) having a structural unit shown by the formula (A) and a compound (b) which generates a radical when irradiated with active rays and has a structure shown by the following formula (B).

This application is a continuation application of U.S. patentapplication Ser. No. 12/759,475, filed on Apr. 13, 2010, and whichclaims priority from Japanese Patent Application No. 2009-097918, filedApr. 14, 2009 and Japanese Patent Application No. 2009-286479, filedDec. 17, 2009, the entire disclosures of which are incorporated hereinby reference.

TECHNICAL FIELD

The invention relates to a photosensitive resin composition used for acircuit formation substrate, in particular, to a photosensitive resincomposition used in a suspension for a hard disk drive which has beenrequired to be larger in capacity or smaller in size in recent years, aswell as to a method for forming a pattern and a circuit formationsubstrate using the same.

BACKGROUND ART

Conventionally, as a surface protection film and an interlayerinsulating film of a semiconductor device, a polyimide resin which hasimproved heat resistance, electric properties, mechanical properties orthe like in combination has been used. However, as a semiconductordevice has become highly integrated and has become larger in size, therehas been a demand for a thinner and smaller package for a sealed resin.Under such circumstances, a method for surface mounting such as LOC(lead-on-chip) and reflow soldering has been adapted, and the demand fora polyimide resin which is improved in mechanical properties, heatresistance or the like has become greater than ever.

A photosensitive polyimide obtained by imparting photosensitiveproperties with a polyimide resin itself has been used. Thisphotosensitive polyimide has advantages that pattern formation steps canbe simplified and the time required for complex production can beshortened. A heat-resistant photoresist using a conventional polyimideor its precursor and the application thereof are well known. Regarding anegative-type photoresist, a polyimide obtained by introducing amethacryloyl group into a polyimide precursor through an ester bond oran ionic bond (see JP-B-3712164, JP-A-2006-173655, JP-A-2008-1876 andJP-A-2008-1877, for example), a soluble polyimide having aphotopolymerizable olefin (see JP-A-H10-36506, JP-A-2000-159887,JP-A-2000-290372, JP-A-2006-328407, JP-B-3860359 and JP-A-2006-328407,for example) and a self-sensitized polyimide having a benzophenoneskeleton and an alkyl group at an ortho group of an aromatic ring towhich a nitrogen atom is bonded (see JP-A-2008-251121 andJP-A-2008-310946, for example), or the like are known.

In recent years, use of such photosensitive polyimide in a circuitformation substrate on a suspension in which a magnetic head of a harddisc drive, such as those mentioned below, is mounted has attractedattention.

As for the magnetic head, in respect of an increased memory capacity, anincreased speed or the like of a hard disc drive, a so-called MR-thinfilm composited head in which a magnetic resistive type MR (MagneticResistive) device and a thin film is integrated has attracted attentioninstead of a conventional MIG (metal-in-gap) or magnetic inductive thinfilm.

In contrast to a conventional head in which reading and writing of amagnetic signal is conducted simultaneously in a single head, in a MRhead, writing and reading are conducted separately in a single head. Asa result, the number of terminals has been doubled (if need arises, aground terminal is added), and hence, a wire for connecting a head and adisk main body is required to be thinner.

However, a wire tends to be corroded as it is rendered thinner. Inaddition, troubles such as difficulty in interface with impedance anddifficulty in mounting of a head tend to occur. In order to solve suchnew problems, a method in which a circuit is directly formed on asuspension in which a head is mounted has been proposed (seeJP-A-S48-16620).

SUMMARY OF THE INVENTION

In the circuit formation substrate as mentioned above, a polyimide resinlayer which has, in combination, improved heat resistance, electricproperties, mechanical properties or the like is used as the interlayerinsulating film or the protective layer of a circuit. However, such useof a polyimide resin layer has the following problems. Specifically, inthe case where the polyimide resin layer has a high water absorbability,if such a circuit formation substrate is incorporated in a hard discdrive main body as a suspension, for example, the dimension of thesubstrate may vary largely due to adsorption and desorption of water toa polyimide resin layer, and as a result, the suspension itself iswarped to cause the accuracy of alignment to be lowered. In addition,since the gap between the disc and the main body is changed, the deviceperformance is deteriorated.

Further, many of polyimide resins with low water absorption containfluorine. In addition, due to the rigid structure thereof, if thepolyimide resin is rendered photosensitive, the solubility thereof in anorganic solvent such as a developer is significantly low. In addition,there are problems that difference in solubility speed between anexposed part and an unexposed part which is sufficient for forming animage cannot be obtained.

The invention has been made in order to solve the above-mentionedconventional problems, and an object thereof is to provide aphotosensitive resin composition which is capable of forming a goodpattern improved in sensitivity and resolution and has appropriateproperties as an interlayer insulating film or a protective film of acircuit formation substrate such as the above-mentioned suspension, aswell as to provide a pattern formation method and a circuit formationsubstrate using this photosensitive resin composition.

According to the invention, the following photosensitive resincomposition or the like are provided. In accordance with a firstembodiment, a photosensitive resin composition for an interlayerinsulating film or a protective film of a substrate for circuitformation is provided, which comprises a polymer (a) having a structuralunit shown by the formula (A)

wherein R¹ is a trivalent or tetravalent organic group, R² is a divalentorganic group, R is a monovalent organic group having a carbon-carbonunsaturated double bond or a group shown by O⁻M, in which M is ahydrogen ion or an ion of a compound having a carbon-carbon unsaturateddouble bond, and at least one of Rs is a monovalent organic group havinga carbon-carbon unsaturated double bond or a group shown by O⁻M, inwhich M is an ion of a compound having a carbon-carbon unsaturateddouble bond, and n is 1 or 2, and a compound (b) which generates aradical when irradiated with active rays and has a structure shown bythe following formula (B)

wherein R³ is a monovalent aromatic or heterocyclic ring, which may havea substituent. In accordance with a second embodiment, thephotosensitive resin composition according to the first embodiment, ismodified so that the polymer (a) has a structural unit shown by thefollowing formula (1)

wherein R¹, R², M and n are as defined in the formula (A). In accordancewith a third embodiment of the invention, the first and secondembodiments are further modified so that, in the structural unit shownby the formula (A), R² is a structure shown by the following formula (2)or (3)

wherein a plurality of R⁴s are independently a fluorine atom or amonovalent organic group having 1 to 10 carbon atoms, which may have anoxygen atom, a sulfur atom or a halogen atom, and m and n areindependently an integer of 0 to 4. In accordance with a fourthembodiment of the present invention, the first, second and thirdembodiments are further modified so that, in the structural unit shownby the formula (A), R² is a structure shown by the following formula (4)

wherein R⁵s are independently a fluorine atom or a trifluoromethylgroup. In accordance with a fifth embodiment of the present invention,the first, second, third and fourth embodiments are further modified sothat the compound (b) is a compound containing an oxime ester structure.In accordance with a sixth embodiment of the present invention, thefifth embodiment is modified so that the compound (b) is shown by thefollowing formula (5)

wherein R¹⁰ to R¹⁶ are independently a monovalent group. In accordancewith a seventh embodiment of the present invention, the sixth embodimentis further modified so that the compound (b) is shown by the followingcompound (6).

In accordance with an eighth embodiment of the present invention, thefirst, second, third, fourth, fifth, sixth and seventh embodiments arefurther modified so that the compound (b) is contained in an amount of0.1 to 20 parts by mass relative to 100 parts by mass of the polymer(a). In accordance with a ninth embodiment of the present invention, thefirst, second, third, fourth, fifth, sixth, seventh and eighthembodiments of the present invention are further modified so that thesubstrate for circuit formation is a supporting substrate of asuspension for a hard disk drive. In accordance with a tenth embodimentof the present invention, a method for forming a pattern is provided,wherein the method includes the steps of (i) applying the photosensitiveresin composition according to any of one of the first, second, third,fourth, fifth, sixth, seventh, eighth and ninth embodiments to asubstrate for circuit formation, followed by drying to form aphotosensitive resin film (ii) exposing the photosensitive resin film tolight (iii) developing the photosensitive resin film after the exposureand (iv) heating the photosensitive resin film after the development. Inaccordance with an eleventh embodiment of the present invention, acircuit formation substrate is provided that comprises, as an interlayerinsulating film or as a protective film, a layer with a patternobtainable by the method for forming a pattern according to the tenthembodiment of the invention. In accordance with a twelfth embodiment ofthe present invention, a circuit formation substrate is provided thatcomprises a supporting substrate, an interlayer insulating film, aconductor film and a protective film in a sequential order, wherein atleast one of the interlayer insulating film and the protective film isformed of the photosensitive resin composition according to any one ofthe first embodiment, the second embodiment, the third embodiment, thefourth embodiment, the fifth embodiment, the sixth embodiment, theseventh embodiment, the eighth embodiment and the ninth embodiment ofthe present invention. In accordance with a thirteenth embodiment of thepresent invention, the eleventh embodiment, of the twelfth embodiment,is further modified so that it is a suspension for a hard disc drive.

The photosensitive resin composition according to the invention iscapable of forming a good pattern on a circuit formation substrate sinceit is improved in sensitivity and resolution even if it contains apolymer having a rigid structure with low thermal expansion propertiesand low hygroscopic expansion properties.

Since the sensitivity of the photosensitive resin composition is high,the method for forming a pattern according to the invention can reducethe production cost due to the reduction of pattern formation time andimproved workability.

The circuit formation substrate according to the invention has an effectof high reliability since it has a pattern with a good shape andexcellent properties as the interlayer insulating layer or theprotective layer of a circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view for explaining steps forforming a pattern of a photosensitive resin composition according to anembodiment of the invention

FIG. 2 is a schematic cross-sectional view for explaining steps forforming a pattern of a photosensitive resin composition according to anembodiment of the invention

FIG. 3 is a schematic cross-sectional view for explaining steps forforming a pattern of a photosensitive resin composition according to anembodiment of the invention

FIG. 4 is a schematic cross-sectional view for explaining steps forforming a pattern of a photosensitive resin composition according to anembodiment of the invention

FIG. 5 is a schematic cross-sectional view for explaining steps forforming a pattern of a photosensitive resin composition according to anembodiment of the invention

FIG. 6 is a schematic cross-sectional view for explaining steps forforming a pattern of a photosensitive resin composition according to anembodiment of the invention

FIG. 7 is a schematic cross-sectional view for explaining steps forforming a pattern of a photosensitive resin composition according to anembodiment of the invention

FIG. 8 is a schematic cross-sectional view for explaining steps forforming a pattern of a photosensitive resin composition according to anembodiment of the invention

FIG. 9 is a schematic cross-sectional view for explaining steps forforming a pattern of a photosensitive resin composition according to anembodiment of the invention and

FIG. 10 is a schematic plan view showing a suspension for a hard discdrive using a photosensitive resin composition in an embodiment of theinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

The embodiment of the photosensitive resin composition for an interlayerinsulating film or a protective film of a circuit formation substrate,the method for forming a pattern using this photosensitive resincomposition and the circuit formation substrate according to theinvention will be explained below in detail with reference to thedrawings. The embodiment is, however, not construed as limiting thescope of the invention.

Component (a) (Polymer)

In the polymer having a structural unit shown by the formula (A), R¹ inthe formula (A) is a trivalent or tetravalent organic group. Generally,this group is a residue, other than a carboxyl group and an acidanhydride group, of tetracarboxylic acid (dianhydride) or tricarboxylicacid (anhydride) used as a raw material. It is preferred that this groupbe a group having an aromatic ring such as a benzene ring. Specificexamples include residues of tetracarboxylic dianhydride, which will bementioned later.

R² in the formula (A) is a divalent organic group. Generally, this groupis a residue other than an amino group of diamine used as a rawmaterial. Specific examples include residues of diamine, which will bementioned later.

In the formula (A), n is 1 or 2. Then n is 2, plural Rs may be the sameor different.

R in the formula (A) is a monovalent group having a carbon-carbonunsaturated double bond or a group shown by O⁻M.

O⁻M is a group formed by ionic bonding of a hydrogen or a monovalentorganic group having a carbon-carbon unsaturated double bond, andoxygen. At least one of Rs is a monovalent organic group having acarbon-carbon unsaturated double bond or a group shown by O⁻M in which Mis a monovalent organic group having a carbon-carbon unsaturated doublebond.

Examples of the group having a carbon-carbon unsaturated double bondinclude a group containing an acryloyl group, a methacryloyl group, anallyl group or the like. In respect of reactivity or the like, a groupcontaining an acryloyl group or a methacryloyl group is preferable.Specific examples of R include a monovalent organic group such as anacryloxyalkyloxy group (CH₂CH—COO—R—O—, wherein R is an alkylene group(an alkylene group having 1 to 10 carbon atoms, for example)), amethacryloxyalkyloxy group (CH₂C(CH₃)—COO—R—O—, wherein R is an alkylenegroup (an alkylene group having 1 to 10 carbon atoms, for example), anacryloxyalkylamino group (CH₂CH—COO—R—NH—, wherein R is an alkylenegroup (an alkylene group having 1 to 10 carbon atoms, for example), anda methacryloxyalkylamino group (CH₂C(CH₃)—COO—R—NH—, wherein R is analkylene group (an alkylene group having 1 to 10 carbon atoms, forexample)). Of these, it is preferred that the group be a group obtainedby allowing a compound having a carbon-carbon unsaturated double bond toform an ester bond with an adjacent CO by covalent bonding. In order toallow the compound having a carbon-carbon unsaturated double bond toform an ester bond with an adjacent carbonyl group, an alcohol havingsuch an organic group and tetracarboxylic dianhydride constituting partof an acid part of the polymer are reacted, for example. As the groupshown by O⁻M in which a compound having a carbon-carbon unsaturateddouble bond is subjected to ionic bonding, a group obtained by ionicbonding of dialkylaminoalkylacrylate or dialkylaminoalkylmethacrylate(for example, each alkyl has 1 to 10 carbon atoms),(CH₂CH—COO—R—NH(C_(n)H_(2n1))₂O⁻, CH₂C(CH₃)—COO—R—NH(C_(n)H_(2n1))₂O⁻

wherein n is a positive integer (for example, 1 to 10) and R is analkylene group (for example, an alkylene group having 1 to 10 carbonatoms)).

Of these, in respect of reactivity, it is preferred that at least one ofRs be a group shown by O⁻M in which a compound having a carbon-carbonunsaturated double bond is subjected to ionic bonding. In particular, apolymer having structural units shown by the following formula (1) ispreferable.

wherein R¹, R², M and n are as defined in the formula (A).

The polymer shown by the above-mentioned formula (A) or the formula (1)can be obtained by the following method, for example. A polyamide acidis obtained by subjecting tetracarboxylic dianhydride and a diaminecompound to addition polymerization. In order to impart the polyamideacid with photosensitivity, an amine compound having an acryloyl groupor a methacryloyl group is added, followed by stirring, whereby thepolyamide acid is ion bonded with the amine compound. The thus obtainedpolymer has a structural unit shown by the formula (A) or the formula(1), and has, without exception, an ion of a compound having an acryloylgroup or a methacryloyl group in the polymer.

In the above-mentioned formula (A) or the formula (1), assuming that thenumber of the structural unit shown by [CO—R¹—CONH—R²—NH] is m, thereare no particular restrictions on the number m. However, it is preferredthat m be 30 to 150. In the polymer, a structural unit other than thestructural unit shown by the above-mentioned formula (A) or the formula(1) may be contained. However, normally, it is preferred that thepolymer be composed of a structural unit shown by the above-mentionedformula (A) or the formula (1) and have a terminal group such as ahydrogen atom, an OH group or the like at the both terminals thereof. Asstructural units other than the structural unit shown by the formula (A)or the formula (1), a structural unit having no side chain such as CORor COO⁻M or a structural unit in which all of COR and COO⁻M are COOH(carboxy group) in the formula (A) or the formula (1), or the like canbe given. As for the content thereof, if the number of the structuralunit other than the structural units shown by the formula (A) or theformula (1) is assumed to be t, it is preferred that t be the same orsmaller than m, and it is preferred that t be 0.3 or less relative tothe total of m and t.

It is preferred that the weight-average molecular weight (Mw) of thecomponent (a) be about 10,000 to 200,000. If the component (a) containsO⁻M, it is preferred that the weight-average molecular weight (Mw) inthe state a compound having a carbon-carbon unsaturated double bond isnot yet bonded by ionic bonding, i.e. in the state of a polyamide acid,be 10,000 to 90,000. Here, the Mw can be measured by the gel permeationchromatography method, and calculated by the standard polystyreneconversion.

Examples of the above-mentioned tetracarboxylic dianhydride include,though not limited thereto, pyromellitic dianhydride,3,3,4,4-benzophenonetetracarboxylic dianhydride,3,3,4,4-biphenyltetracarboxylic dianhydride, 4,4-oxydiphthalicdianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride,1,4,5,8-naphthalanetetracarboxylic dianhydride, 4,4-sulfonyldiphthalicdianhydride and 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride.

Examples of the diamine compound includes, though not limited thereto,aromatic diamines such as p-phenylenediamine, m-phenylenediamine,2,2-dimethyl-4,4-diaminobiphenyl, p-xylylenediamine, m-xylylenediamine,1,5-diaminonaphthalene, benzidine, 3,3-dimethoxybenzidine, 4,4-(or 3,4-,3,3-, 2,4)diaminodiphenylmethane, 4,4-(or 3,4-, 3,3-,2,4)diaminodiphenylether, 4,4-(or 3,4-, 3,3-,2,4)diaminodiphenylsulfone, 4,4-(or 3,4-, 3,3-,2,4)diaminodiphenylsulfide, 4,4-benzophenonediamine,3,3-benzophenonediamine, 4,4-di(4-aminophenoxy)phenylsulfone,4,4-bis(4-aminophenoxy)biphenyl, 1,4-bis(4-aminophenoxy)benzene,1,3-bis(4-aminophenoxy)benzene,1,1,1,3,3,3-hexafluoro-2,2-bis(4-aminophenyl)propane,2,2-bis(trifluoromethyl)benzidine,2,2-bis[4-(4-aminophenoxy)phenyl]propane,3,3-dimethyl-4,4-diaminodiphenylmethane,3,3,5-tetramethyl-4,4-diaminodiphenylmethane,4,4-di(3-aminophenoxy)phenylsulfone, 3,3-diaminodiphenylsulfone,2,2-bis(4-aminophenyl)propane, 5,5-methylene-bis-(anthranililic acid),3,5-diaminobenzoic acid, 3,3-dihydroxy-4,4-diaminobiphenyl,3,3-dimethyl-4,4-diaminobiphenyl, 2,2-dimethyl-4,4-diaminobiphenyl, and3,3-dimethyl-4,4-diaminobiphenyl-6,6-disulfonic acid heterocyclicdiamines such as 2,6-diaminopyridine, 2,4-diaminopyridine,2,4-diamino-s-triazine, 2,7-diaminobenzofuran, 2,7-diaminocarbazole,3,7-diaminophenothiazine, 2,5-diamino-1,3,4-thiaziazole, and2,4-diamino-6-phenyl-s-triazine and aliphatic diamines such astrimethylene diamine, tetramethylene diamine, hexamethylene diamine,2,2-dimethylpropylene diamine, and diaminopolysiloxane shown by thefollowing formula (4)

wherein R⁵, R⁶, R⁷ and R⁸ are independently an alkyl group having 1 to 6carbon atoms, and o and p are independently an integer of 1 to 10.

Each of the tetracarboxlic dianhydride and the diamine compound asmentioned above is used singly and/or in combination of two or more.

Of the above-mentioned diamine compounds, one having a diamine residueshown by the following formula (2) or (3) is preferable since not onlyit gives preferred transparency as the photosensitive resin but alsogives preferred low thermal expansion properties and low hygroscopicexpansion properties which are preferable for use as the interlayerinsulating film or the protective film of a suspension.

wherein plural R⁴s are independently a fluorine atom or a monovalentorganic group having 1 to 10 carbon atoms which may have an oxygen atom,a sulfur atom or a halogen atom, and m and n are independently aninteger of 0 to 4.

Of these, in view of low hygroscopic expansion properties, it ispreferred that R⁴ be a group selected from a methyl group, an ethylgroup, an isopropyl group, a t-butyl group, a fluorine atom and atrifluoromethyl group. It is particularly preferred that R⁴ be afluorine atom or a trifluoromethyl group.

Further, in the formula (2), in respect of imparting low thermalexpansion properties and low hygroscopic expansion properties, it ispreferred that two R⁴s be positioned at the ortho position relative tothe bond connecting two benzene rings. Of these structures, a diamineresidue shown by the following formula (4) is preferable.

wherein R⁵s are independently a fluorine atom or a trifluoromethylgroup.

As the amine having an acryloyl group or a methacryloyl group to beadded in order to impart the polyamide acid with photosensitivity,N,N-dialkylaminoalkyl(meth)acrylate such as N,N-diethylaminopropylmethacrylate, N,N-dimethylaminopropyl methacrylate,N,N-diethylaminopropyl acrylate, N,N-diethylaminoethyl methacrylate, orthe like can be given. The amines are, however, not limited thereto. Itis preferred that the amine having an acryloyl group or a methacryloylgroup of these be added in an amount of 20 to 200 parts by mass relativeto 100 parts by mass of the above-mentioned polyamide acid to form thecomponent (a).

Component (b) (Sensitizer)

The component (b) is a compound which generates a radical by irradiationof active rays and contains a structure shown by the following formula(B)

wherein R³ is a monovalent aromatic or heterocyclic ring, which may havea substituent.

There are no particular restrictions on the component (b) insofar as itis a compound which has the above structure and is capable of generatinga radical upon exposure to active rays.

For example, other than the compounds classified into oxime estersmentioned later, the following compounds can be given as preferablecompounds.

N,N-tetraalkyl-4,4-diamino-benzophenone such as benzophenone andN,N-tetramethyl-4,4-diaminobenzophenone(Michlesr ketone), aromaticketones such as2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1,2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propane-1,quinines which form a condensed ring with an aromatic ring such asalkylanthraquinone, benzoin ether compounds such as benzoin alkyl ether,a benzoin compound such as benzoin and alkylbenzoin, benzyl derivativessuch as benzyl dimethyl ketal or a compound shown by the followingformula (10).

wherein R⁵⁰ is an alkyl group having 1 to 20 carbon atoms an alkyl grouphaving 2 to 20 carbon atoms which contains one or more oxygen atomstherein an alkoxy group having 1 to 12 carbon atoms a phenyl group whichis substituted by an alkyl group having 1 to 4 carbon atoms a phenylgroup a phenyl group which is substituted by an alkyl group having 1 to20 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, a halogen,a cyclopentyl group, a cyclohexyl group, an alkenyl group having 1 to 12carbon atoms, an alkyl group having 2 to 18 carbon atoms which containsone or more oxygen atoms therein and/or an alkyl group having 1 to 4carbon atoms or a biphenylyl group, R⁵¹ is a group shown by the formula(11) or the same group as the above-mentioned R⁵⁰, R⁵² to R⁵⁴ areindependently an alkyl group having 1 to 12 carbon atoms, an alkoxygroup having 1 to 12 carbon atoms or a halogen.

wherein R⁵⁵ to R⁵⁷ are the same as R⁵² to R⁵⁴ in the above-mentionedformula (10).

Of these, oxime esters are more preferable since they are particularlyimproved in sensitivity, and give a significantly good pattern in aphotosensitive resin composition containing a polymer having a diamineresidue shown by the above-mentioned (2) or (3), in particular, apolymer containing a diamine residue shown by the formula (4). Inparticular, in the case of the component (a) having a diamine residueshown by the formula (4), there may be a case where good sensitivitycharacteristics cannot be obtained. In order to attain good sensitivityand residual film ratio in such component (a), oxime esters shown by thefollowing formula (5) are particularly preferable.

wherein R¹⁰ to R¹⁶ are independently a monovalent group.

As for the above-mentioned monovalent organic group, a preferable groupvaries depending on the substituent. The following can be given, forexample.

R¹⁰ is a phenyl group (it may be substituted by one or more of an alkylgroup having 1 to 6 carbon atoms, a phenyl group, a halogen atom, —OR³⁰,—SR³¹ or N(R³²)(R³³), in which R³⁰ to R³³ are an alkyl group having 1 to20 carbon atoms), an alkyl group having 1 to 20 carbon atoms (when thenumber of carbon atoms of the alkyl group is 2 to 20, it may have one ormore oxygen atoms between carbon atoms constituting the main chainand/or may be substituted by one or more hydroxyl groups), a cycloalkylgroup having 5 to 8 carbon atoms, an alkanoyl group having 2 to 20carbon atoms, a benzoyl group (it may be substituted by one or more ofan alkyl group having 1 to 6 carbon atoms, a phenyl group, —OR³⁰, —SR³¹or N(R³²)(R³³), in which R³⁰ to R³³ are an alkyl group having 1 to 20carbon atoms), an alkoxycarbonyl group having 2 to 12 carbon atoms (whenthe number of carbon atoms of the alkoxy group is 2 to 11, the alkoxygroup may have one or more oxygen atoms between carbon atomsconstituting the main chain and/or may be substituted by one or morehydroxyl groups), a phenoxycarbonyl group (it may be substituted by oneor more of an alkyl group having 1 to 6 carbon atoms, a phenyl group, ahalogen atom, —OR³⁰ or N(R³²)(R³³), in which R³⁰, R³² and R³³ are analkyl group having 1 to 20 carbon atoms, a cyano group, a nitro group,—CON(R³²)(R³³), a haloalkyl group having 1 to 4 carbon atoms, —S(O)m-R²⁰(R²⁰ is an alkyl group having 1 to 6 carbon atoms or an aryl grouphaving 6 to 12 carbon atoms which may be substituted by an alkyl grouphaving 1 to 12 carbon atoms, and m is 1 or 2), an alkoxysulfonyl grouphaving 1 to 6 carbon atoms, an aryloxysulfonyl group having 6 to 10carbon atoms or a diphenylphosphinoyl group.

R¹¹ is an alkanoyl group having 2 to 12 carbon atoms (it may besubstituted by one or more of a halogen atom or a cyano group), analkenoyl group having 4 to 6 carbon atoms of which the double bond isnot conjugated with a carbonyl group, a benzoyl group (it may besubstituted by one or more of an alkyl group having 1 to 6 carbon atoms,a halogen atom, a cyano group, —OR³⁰, —SR³¹— or N(R³²)(R³³)), analkoxycarbonyl group having 2 to 6 carbon atoms, or a phenoxycarbonylgroup (it may be substituted by one or more of an alkyl group having 1to 6 carbon atoms or a halogen atom),

R¹², R¹³, R¹⁴, R¹⁵ and R¹⁶ are independently a hydrogen atom, a halogenatom, an alkyl group having 1 to 12 carbon atoms, a cyclopentyl group, acyclohexyl group or a phenyl group (it may be substituted by one or moreof OR³⁰, —SR³¹ or N(R³²)(R³³), a benzyl group, a benzoyl group, analkanoyl group having 2 to 12 carbon atoms, an alkoxycarbonyl grouphaving 2 to 12 carbon atoms (when the number of carbon atoms is 2 to 11,the alkoxy group may have one or more oxygen atoms between carbon atomswhich constitute the main chain and/or may be substituted by one or morehydroxyl groups), a phenoxycarbonyl group, —OR³⁰ (—OR³⁰ may be bonded toone of carbon atoms in the phenyl ring or the substituents for thephenyl ring to form a five- or six-membered ring), —SR³¹ (—SR³¹ may bebonded to one of carbon atoms in the phenyl ring or the substituents forthe phenyl ring to form a five- or six-membered ring), —S(O)R³¹ (—SR³¹may be bonded to one of carbon atoms in the phenyl ring or thesubstituents for the phenyl ring to form a five- or six-membered ring),—SO₂R³¹ (—SR³¹ may be bonded to one of carbon atoms in the phenyl ringor the substituents for the phenyl ring to form a five- or six-memberedring), —N(R³²)(R³³)(—NR³² and/or NR³³ may be bonded to one of carbonatoms in the phenyl group or in the substituent for the phenyl group toform a five- or six-membered ring), and at least one of R¹², R¹³, R¹⁴,R¹⁵ and R¹⁶ is OR³⁰, —SR³¹ or N(R³²)(R³³),

R³⁰ is a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, asubstituted alkyl group having 2 to 6 carbon atoms the substituent isformed of one or more of a hydroxyl group, a mercapto group, a cyanogroup, an alkoxyl group having 1 to 4 carbon atoms, an alkenyloxy grouphaving 3 to 6 carbon atoms, a 2-cyanoethoxy group, a2-(alkoxycarbonyl)ethoxy group having 4 to 7 carbon atoms, analkylcarbonyloxy group having 2 to 5 carbon atoms, a phenylcarbonyloxygroup, a carboxyl group or an alkoxycarbonyl group having 2 to 5 carbonatoms, an alkyl group having 2 to 6 carbon atoms having one or moreoxygen atoms between carbon atoms constituting the main chain, analkanoyl group having 2 to 8 carbon atoms, —(CH₂CH₂O)_(n)H (wherein n isan integer of 1 to 20), an alkenyl group having 3 to 12 carbon atoms, analkenoyl group having 3 to 6 carbon atoms, a cyclohexyl group, a phenylgroup (it may be substituted by a halogen atom, an alkyl group having 1to 12 carbon atoms or an alkoxy group having 1 to 4 carbon atoms), aphenylalkyl group having 7 to 9 carbon atoms, or Si(R⁴⁰)_(r)(R⁴¹)_(3-r)(wherein R⁴⁰ is an alkyl group having 1 to 8 carbon atoms, R⁴¹ is aphenyl group, and r is an integer of 1 to 3)

R³¹ is a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, analkenyl group having 3 to 12 carbon atoms, a cyclohexyl group, asubstituted alkyl group having 2 to 6 carbon atoms the substituent isformed of one or more of a hydroxyl group, a mercapto group, a cyanogroup, an alkoxyl group having 1 to 4 carbon atoms, an alkenyloxy grouphaving 3 to 6 carbon atoms, a 2-cyanoethoxy group, a2-(alkoxycarbonyl)ethoxy group having 4 to 7 carbon atoms, analkylcarbonyloxy group having 2 to 5 carbon atoms, a phenylcarbonyloxygroup, a carboxyl group or an alkoxycarbonyl group having 2 to 5 carbonatoms, an alkyl group having 2 to 12 carbon atoms having one or moreoxygen atoms or sulfur atoms between carbon atoms constituting the mainchain, a phenyl group (it may be substituted by a halogen atom, an alkylgroup having 1 to 12 carbon atoms or an alkoxyl group having 1 to 4carbon atoms) or a phenylalkyl group having 7 to 9 carbon atoms

R³² and R³³ are independently are a hydrogen atom, an alkyl group having1 to 12 carbon atoms, a hydroxyalkyl group having 2 to 4 carbon atoms,an alkoxyalkyl group having 2 to 10 carbon atoms, an alkenyl grouphaving 3 to 5 carbon atoms, a cycloalkyl group having 5 to 12 carbonatoms, a phenylalkyl group having 7 to 9 carbon atoms, a phenyl group(it may be substituted by one or more of an alkyl group having 1 to 12carbon atoms or an alkoxy group having 1 to 4 carbon atoms), an alkanoylgroup having 2 to 3 carbon atoms, an alkenoyl group having 3 to 6 carbonatoms, or a benzoyl group, or R³² and R³³ together form an alkylenegroup having 2 to 6 carbon atoms (it may have one or more oxygen atomsor NR³⁰— between carbon atoms constituting the main chain and/or may besubstituted by one or more of a hydroxyl group, an alkoxyl group having1 to 4 carbon atoms, an alkanoyloxy group having 2 to 4 carbon atoms ora benzoyloxy group).

In particular, among them, one in which at least one of R¹², R¹³, R¹⁴,R¹⁵ and R¹⁶ is SR³¹ is preferable since it is particularly improved insensitivity and residual film ratio.

In the formula (5), R¹⁰ is preferably an alkyl group having 1 to 10carbon atoms, more preferably an alkyl group having 4 to 7 carbon atoms,and particularly preferably a hexyl group. It is preferred that four ofR¹² to R¹⁶ are hydrogen and it is more preferred that R¹², R¹³, R¹⁵ andR¹⁶ are hydrogen and the remaining is SR³¹. This SR³¹ is preferably acyclohexyl group, a phenyl group, or a phenylalkyl group having 7 to 10carbon atoms, more preferably a phenyl group or a phenylalkyl grouphaving 7 to 10 carbon atoms, with a phenyl group being particularlypreferable.

Further, as a compound which serves not to adversely affect a lowhygroscopic expansion coefficient or often further lower such lowhygroscopic expansion coefficient, which is appropriate for use in aprotective film of a hard disc suspension, a compound having a structureshown by the following formula (6) is significantly preferable.

It is preferred that the above-mentioned component (b) be added in anamount of 0.1 to 20 parts by mass relative to 100 parts by mass of theabove-mentioned component (a). If the amount is less than 0.1 part bymass, photosensitivity may become poor. If the amount exceeds 20 partsby mass, the mechanical properties of the film may be deteriorated. Itis more preferred that the amount of the component (b) be 0.5 to 10parts by mass.

Component (c) (Solvent)

In the invention, for synthesizing a polyamide acid and as a componentof the photosensitive resin composition, a solvent is normally used.Usable solvents include acetone, methyl ethyl ketone, toluene,chloroform, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol,2-butanol, t-butanol, ethylene glycol monomethyl ether, propylene glycolmonomethyl ether, xylene, tetrahydrofuran, dioxane,N,N-dimethylacetoamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone,γ-butyrolactone, dimethylsulfoxide, ethylene carbonate, propylenecarbonate and sulfolane. These organic solvents are used singly or incombination of two or more.

It is preferred that the component (c) be used in an amount of 100 to500 parts by mass relative to 100 parts by mass of the above-mentionedcomponent (a).

The photosensitive resin composition of the invention is normallyprovided in the form of varnish. If need arises, a sensitizer, alight-shielding agent, a polymerization inhibitor, a cross-linkingagent, a dissolution accelerator, a stabilizer, an adhesion aid or thelike may be added to the photosensitive resin composition.

Here, the polymerization inhibitor is used not only to improve theresolution of this photosensitive resin composition but also to enhancethe storage stability thereof. Examples of such radical polymerizationinhibitor or the radical polymerization suppressor includep-methoxyphenol, diphenyl-p-benzoquinone, benzoquinone, hydroquinone,pyrogallol, phenothiazine, resorcinol, orthodinitrobenzene,paradinitrobenzene, methadinitrobenzene, phenanthraquinone,N-phenyl-1-naphthylamine, N-phenyl-2-naphthylamine, cupferron,phenothiazine, 2,5-toluquinone, tannic acid, parabenzyl aminophenol andnitrosoamine. These may be used either singly or in combination of twoor more.

The radical polymerization inhibitor or the radical polymerizationsuppressor is used preferably in an amount of 0.01 to 30 parts by mass,more preferably 0.05 to 10 parts by mass, relative to the total amount,i.e. 100 parts by mass, of the component (a). If the amount is less than0.01 parts by mass, stability during storage may be deteriorated. Anamount exceeding 30 parts by mass results in lowering ofphotosensitivity and mechanical properties.

As the dissolution accelerator, a sulfonamide derivative is preferable,for example. Examples of the sulfonamide derivative include benzenesulfoneamide, toluene sulfoneamide, methoxybenzene sulfoneamide, benzenesulfonylanilide, toluene sulfonylanilide,methoxy-toluenesulfonylanilide, acetyl-toluenesulfonylanilide,toluenesulfonyl-N-methylamide, toluenesulfonyl-N-ethylamide,toluenesulfonyl-N-propylamide, toluenesulfonyl-N-butylamide,toluenesulfonyl-N-phenylamide, toluenesulfonyl-N-dimethylamide,toluenesulfonyl-N-diethylamide and toluenesulfonyl-N-diphenylamide. Ofthese, N-phenylbenzene sulfoneamide is preferable since it isparticularly effective.

The amount of the dissolution accelerator is preferably 2 to 30 parts bymass, more preferably 3 to 15 parts by mass, relative to 100 parts bymass of the above-mentioned component (a).

If the amount of the dissolution accelerator is less than 2 parts bymass, the photosensitive resin is not dissolved in a developer,resulting in difficulty in forming a pattern. On the other hand, anamount exceeding 30 parts by mass is not preferable since a formedpattern becomes brittle.

For example, the composition of the invention may be formed only of thecomponents (a) and (b) in an amount of 75 wt or more, 85 wt or more, 95wt or more or 100 wt, excluding the component (c). In addition to thesecomponents, the composition of the invention may contain a substancewhich does not impair novel and basic properties of the invention suchas those mentioned above as additives.

[Method for Forming a Pattern]

The method for forming a pattern according to the invention will beexplained. In the method for forming a pattern according to theinvention, the above-mentioned photosensitive resin composition isapplied to a supporting substrate of a suspension for a hard disc drive,e.g. a stainless substrate for suspension formation, by spraying, screenprinting, rotational coating, for example. Subsequently, an organicsolvent in the photosensitive composition is removed by heating anddrying, thereby to obtain a photosensitive resin film which is anon-sticky coating film. This coating film is irradiated with activerays in the shape of a pattern, thereby to form, for example, athrough-hole pattern. As the active rays for irradiation, ultravioletrays, far ultraviolet rays, visible rays, electronic rays, -rays or thelike can be given. After the irradiation of active rays, non-irradiatedparts are removed with a suitable developer, thereby to obtain a desiredrelief pattern.

Although there are no particular restrictions on the type of adeveloper, a fire-resistant solvent such as 1,1,1-trichloroethane, anaqueous alkaline solution such as an aqueous solution of sodiumcarbonate and an aqueous solution of tetramethylammonium hydroxide, agood solvent such as N,N-dimethylformamide, dimethylsulfoxide,N,N-dimethylacetoamide, N-methyl-2-pyrrolidone and γ-butyrolactone, anda mixed solvent of these good solvents with a poor solvent such as alower alcohol, water and aromatic hydrocarbon. After the development,rinsing is conducted with a poor solvent or the like if need arises.

A relief pattern obtained by the above-mentioned process is heated at 80to 400° C. for 5 to 300 minutes, for example, to allow the ring closingof the imide, thereby to obtain a polyimide pattern.

The method for forming a pattern according to the invention can shortenthe time required for forming a pattern, resulting in an improvedworkability since the sensitivity of the photosensitive resin film ishigh. In addition, the production cost can also be reduced.

Subsequently, as one example of the method for forming a patternaccording to the invention, a process in which a pattern is formed on asuspension of a hard disc drive will be explained below with referenceto the drawings.

FIGS. 1 to 9 are schematic cross-sectional views for explaining aprocess for forming a photosensitive resin pattern. In these FIGS. 1 to9, for example, stainless foil is prepared as a supporting substrate 1constituting a suspension (FIG. 1). Subsequently, on this supportingsubstrate 1, the above-mentioned photosensitive resin composition isapplied by means of a spin coater or the like (FIG. 2), followed byexposure and development to form an insulating layer 2 (FIG. 3).

Subsequently, in order to allow a plated film to grow on the insulatinglayer 2, which is an insulator, a seed layer 3 is formed as a backingmetal layer (FIG. 4). As the seed layer 3, two layers of a chromium thinfilm and a copper thin film can be formed by a high-frequency sputteringmethod or the like. Subsequently, a resist (photosensitive resincomposition) 4 is applied to the seed layer 3, and the resultant isexposed to light with a prescribed pattern, followed by development(FIG. 5). In an opening 5 of a resist pattern, a multilayer circuitconductor of copper, nickel, gold or the like is sequentially stacked byelectroplating, thereby to form a circuit layer 6 (FIG. 6).

After the circuit layer 6 is formed, the resist 4 is peeled off, and theseed layer 3 is removed by etching (FIG. 7). Subsequently, in order toprotect the circuit layer 6, the same photosensitive resin compositionas mentioned above is applied to the circuit layer 6, followed byexposure and development, thereby to form a protective layer 7 (FIG. 8).Thereafter, a cover 8 for covering a prescribed part of the protectivelayer 7 and the supporting substrate 1 is provided, whereby gimbal canbe formed (FIG. 9).

[Circuit Formation Substrate]

The photosensitive resin composition according to the invention is usedfor forming a pattern by the above-mentioned method for forming apattern. The resulting pattern is used as an interlayer insulating filmor a protective film of a circuit formation substrate such as asuspension for a hard disc drive and a flexible circuit board. Inparticular, the photosensitive resin composition of the invention isused as a material for an interlayer insulating film formed on a metalsubstrate such as a stainless substrate of a suspension for a hard discdrive or as a material for forming a film for protecting electric signallines formed on the metal substrate or the resin substrate.

For example, the suspension for a hard disc drive according to theinvention includes a supporting substrate such as stainless steel, aninterlayer insulating film obtainable by the above-mentionedphotosensitive resin composition, a conductive layer such as a copperlayer, and a protective layer obtainable by the photosensitive resincomposition in a sequential order. On the interlayer insulating film, acopper layer may be formed through a chromium layer or a titanium layer.

FIG. 10 is a schematic plan view showing one example of a suspension ofa hard disc drive in which a pattern is formed using the photosensitiveresin composition according to the invention. In FIG. 10, a suspension10 is provided with a magnetic head having a function of writing andreading data to a magnetic disc and serves to control a gap between themagnetic disc and the magnetic head to several tens nanometers with ahigh degree of accuracy. The suspension 10 is formed of a plate-likemember 11 which is made of stainless steel or the like. At the tip ofthe plate-like member 11 constituting the suspension 10, the gimbal 13is integrally formed by a notch 12. On the gimbal 13, a slider (notshown) having a magnetic head is fixed.

On the plate-like member 11, an insulating layer (not shown) made fromthe photosensitive resin composition is formed. A prescribed patterncircuit formed of a copper conductor layer 14 is mounted thereon.Further, a protective layer 15 made from the photosensitive resincomposition is formed. Since a prescribed pattern circuit is mounted onthe plate-like member 11, this suspension 10 is called the so-called“suspension with a circuit”.

The photosensitive resin composition of the invention can be used forthe insulating layer or the protective film.

EXAMPLES

The invention will be explained in more detail according to Examples andComparative Examples, which should not be construed as limiting thescope of the invention.

Synthesis Example 1 Synthesis of Polyamide Acid

To 150 ml of N-methyl-2-pyrrolidone, 5.4 g (50 mmol) ofp-phenylenediamine and 16.0 g (50 mmol) of2,2-bis(trifluoromethyl)benzidine were added and dissolved. Thereafter,29.4 g (100 mmol) of 3,3,4,4-biphenyltetracarboxlic dianhydride wasadded to allow the resultant to be polymerized, whereby a polyamide acidwith a weight average molecular weight calculated by a standardpolystyrene conversion of 41,400 was obtained. This is referred to as apolymer solution I.

Synthesis Example 2

Synthesis was conducted in the same manner as in Synthesis Example 1except that 2,2-bis(trifluoromethyl)benzidine used in Synthesis Example1 was replaced by an equivalent molar amount of 2,2-dimethylbenzidine.

As a result of a standard polystyrene conversion, the resultingpolyamide acid had a weight average molecular weight of 51,500. This isreferred to as a polymer solution II.

Synthesis Example 3

Synthesis was conducted in the same manner as in Synthesis Example 1except that 2,2-bis(trifluoromethyl)benzidine used in Synthesis Example1 was replaced by an equivalent molar amount of2,3,5,6-tetramethyl-1,4-phenylenediamine.

As a result of a standard polystyrene conversion, the resultingpolyamide acid had a weight average molecular weight of 36,100. This isreferred to as a polymer solution III.

Synthesis Example 4

Synthesis was conducted in the same manner as in Synthesis Example 1except that p-phenylenediamine used in Synthesis Example 1 was replacedby an equivalent molar amount of 2,2-bis(trifluoromethyl)benzidine.

As a result of a standard polystyrene conversion, the resultingpolyamide acid had a weight average molecular weight of 47,900. This isreferred to as a polymer solution IV.

Synthesis Example 5

Synthesis was conducted in the same manner as in Synthesis Example 1except that 3,3,4,4-biphenyltetracarboxlic dianhydride used in SynthesisExample 1 was replaced by an equivalent molar amount of pyromelliticdianhydride and p-phenylenediamine was replaced by an equivalent molaramount of 2,2-dimethylbenzidine.

As a result of a standard polystyrene conversion, the resultingpolyamide acid had a weight average molecular weight of 38,900. This isreferred to as a polymer solution V.

Synthesis Example 6 Synthesis of Polyimideamide Acid Ester

In a 0.2 I-capacity flask provided with a stirrer and a thermometer,29.4 g (100 mmol) of 3,3,4,4-biphenyltetracarboxylic dianhydride and28.6 g (220 mmol) of 2-hydroxyethyl methacrylate were dissolved in 100 gof N-methylpyrrolidone. Then, 1,8-diazabicycloundecene was added in acatalytic amount, and the resultant was heated at 60° C. for 2 hours,and then stirred for 15 hours at room temperature (25° C.) to conductesterification. Thereafter, while cooling on ice, 25.9 g (220 mmol) ofthionyl chloride was added. Then, the temperature was returned to roomtemperature, and the reaction was conducted for 2 hours, thereby toobtain a solution of an acid chloride. Subsequently, a 1 l-capacityflask provided with a stirrer and a thermometer was charged with 150 gof N-methylpyrrolidone. Then, 10.6 g (50 mmol) of 2,2-dimethylbenzidineand 16.0 g (50 mmol) of 2,2-bis(trifluoromethyl)benzidine were added,followed by stirring for dissolution. Then, 26.2 g (220 mmol) ofpyridine was added. While keeping the temperature at 0 to 5° C., theacid chloride solution which had been in advance was added dropwise overa period of 30 minutes, and the resultant was stirred for 30 minutes.This reaction liquid was added dropwise to distilled water. Aprecipitate was collected by filtration and dried under reduced pressureto obtain a polyamide acid ester. As a result of a standard polystyreneconversion, the resulting polyamide acid ester had a weight averagemolecular weight of 19,400. This is referred to as a polymer VI.

A polymer solution obtained by dissolving 100 parts by mass of polymerVI in 300 parts by mass of N-methyl-2-pyrrolidone is referred to as apolymer solution VI.

Examples 1 to 13 1. Preparation of a Photosensitive Resin Composition

To the polymer solutions I to V shown in Table 1,N,N-dimethylaminopropyl methacrylate (DAPM) was added in an equivalentmolar amount as that of the carboxy group of the amide acid used.Further, as the component (b), a prescribed amount of a sensitizer shownin Table 1 was added, followed by stirring, whereby photosensitive resinsolutions were obtained. The numeral value of the component (b) in theparenthesis in Table 1 is the part by mass of the component (b) when themass of the polyamide acid in the polymer solution is taken as 100.

As for the polymer solution VI, the component (b) alone was used andstirred similarly to obtain a photosensitive resin solution.

TABLE 1 Component (a)(c) Component (b) Example 1 Polymer solution I DAPMB1 (3) Example 2 Polymer solution I DAPM B2 (5) Example 3 Polymersolution II DAPM B1 (3) Example 4 Polymer solution II DAPM B3 (5)Example 5 Polymer solution III DAPM B2 (5) Example 6 Polymer solutionIII DAPM B4 (5) Example 7 Polymer solution IV DAPM B1 (5) Example 8Polymer solution IV DAPM B2 (5) Example 9 Polymer solution IV DAPM B4(5) Example 10 Polymer solution V DAPM B1 (5) Example 11 Polymersolution V DAPM B3 (5) Example 12 Polymer solution VI B1 (5) Example 13Polymer solution VI B4 (5) B1 A compound having a structure shown by theformula (6) B2 DAROCUR TPO (2,4,6-trimethylbenzoyl-diphenyl-phosphineoxide) manufactured by Ciba Specialty Chemicals B3 Benzyl dimethyl ketalB4 IRGACURE OE-02(ethanone-1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazole-3-yl]-1-(o-acetyloxime)

2. Evaluation of the Photosensitive Resin Composition 2-1.Photosensitivity and Resolution

The resulting photosensitive resin composition was applied to astainless substrate by rotational coating, and dried on a hot plate at90° C. for 3 minutes, whereby a photosensitive resin film with a filmthickness of 12 μm was obtained. This photosensitive resin film wasexposed to light by means of a high-pressure mercury lamp through aphotomask. Subsequently, the film was then heated on a hot plate at 110°C. for 1 minute, and immediately immersed in a developer ofN-methyl-2-pyrrolidone to allow unexposed parts to be dissolved.

After the unexposed parts were completely dissolved, the substrate wastaken out of the developer, and rinsed with isopropyl alcohol.Evaluation was made on the minimum exposure amount (sensitivity) whichwas required for the formation of a pattern, i.e. which allows a film inthe exposed part to be dissolved in an amount of less than 10, as wellas the minimum value of the mask dimension in an opening in the form ofa square hole as resolution. The results are shown in Table 2.

TABLE 2 Sensitivity Resolution mJ · cm⁻² μm Example 1 100 5 Example 2250 7 Example 3 200 7 Example 4 300 6 Example 5 350 7 Example 6 250 6Example 7 100 7 Example 8 250 6 Example 9 150 7 Example 10 150 6 Example11 200 5 Example 12 100 6 Example 13 150 6

2-2. Thermal Expansion Coefficient and Hygroscopic Expansion Coefficient

The resulting photosensitive resin composition was applied to siliconwafer by spin coating, and the resultant was heated at 90° C. for 3minutes, whereby a coating film with a thickness of 20 μm was formed.

Thereafter, the coating film was heated in an inert gas oven in anitrogen atmosphere at 200° C. for 30 minutes. The film was furtherheated at 350° C. for one hour to obtain a cured film. The cured filmwas immersed in an aqueous solution of hydrofluoric acid together with asilicon substrate. The cured film was peeled off from the substrate,rinsed and dried. Thereafter, the thermal expansion coefficient and thehygroscopic expansion coefficient were measured by the following method.The results are shown in Table 3.

(1) Thermal Expansion Coefficient

The film which had been peeled off was cut into a width of 2 mm and alength of 20 mm to obtain a specimen for evaluation. By using athermomechanical analyzer (TMA/SS6000 manufactured by Seiko InstrumentsInc.), an average coefficient of linear expansion between 100 to 200° C.at a heating rate of 5° C./min and a tensile load of 10 g/0.02 mm² wasmeasured.

(2) Hygroscopic Expansion Coefficient

The film which had been peeled off was cut into a width of 5 mm and alength of 20 mm to obtain a specimen for evaluation. By using athermomechanical analyzer (TMA8310 manufactured by Rigaku Corp.), ahydroscopic expansion coefficient was measured under water vaporatmosphere. The specimen was kept at a temperature of 25° C. and ahumidity of 20 RH for 2 hours for stabilization. Subsequently, thespecimen was kept at a humidity of 80 RH, and this state was maintainedfor 1 hour until the specimen was stabilized. A difference in specimenlength was divided by a variation in humidity, thereby to obtain ahydroscopic expansion coefficient (tensile load 25 g/0.05 mm²).

TABLE 3 Thermal expansion Hygroscopic expansion coefficient coefficientppm · K⁻¹ ppm⁻¹ Example 1 16 10 Example 2 15 14 Example 3 18 14 Example4 18 16 Example 5 12 15 Example 6 13 14 Example 7 19 9 Example 8 17 14Example 9 18 11 Example 10 12 9 Example 11 11 13 Example 12 16 11Example 13 16 15

As shown in Table 3, in Examples 1 to 13, a cured film with a lowthermal expansion and a low hygroscopic expansion could be obtained.Further, when B1 was used as the component (b), better results wereobtained with a further lower hygroscopic expansion coefficient.

2-3. Warping

The resulting photosensitive composition was applied to a stainlessplate (SUS 304 with a thickness of 20 μm) by means of an applicator. Theresultant was dried by heating in an oven at 105° C. for 4 minutes,whereby a coating film with a thickness of about 20 μm was formed. Thefilm, together with the substrate, was cut into an 8 cm 8 cm square. Thefilm which had been cut was heated in an inert gas oven in a nitrogenatmosphere at 200° C. for 30 minutes. Thereafter, the film was heated at350° C. for 1 hour to cause the film to be cured.

The center of the substrate was pushed to a plane surface, and thedegree of warping was measured for the four corners of the stainlessplate. The average value of the thus measured warping degrees was takenas warping. A stainless plate of which the four corners were warped inthe direction of the coating surface was indicated as and a stainlessplate of which the four corners were warped in the direction opposite tothe coating surface was indicated as -. The results are shown in Table4.

TABLE 4 arping of stainless plate mm Example 1 1 Example 3 1 Example 6−1 Example 7 2 Example 9 1 Example 10 −2 Example 12 0

As shown in the table, each of the stainless plates underwent warpingwithin a range of 2 mm, which was preferable for use as a suspension fora hard disc drive.

Comparative Synthesis Example 1

Synthesis was conducted in the same manner as in Synthesis Example 1,except that the 3,3,4,4-biphenyltetracarboxlic dianhydride used inSynthesis Example 1 was replaced by an equivalent molar amount ofoxydiphthalic anhydride and all of the amine components were replaced byan equivalent molar amount of 4,4-diaminodiphenyl ether.

As a result of a standard polystyrene conversion, the resultingpolyamide acid had a weight average molecular weight of 51,100. This isreferred to as a polymer solution VII.

Comparative Examples 1 to 5

To the polymer solutions I, III, V and VII, N,N-dimethylaminopropylmethacrylate (DAPM) was added in an equivalent molar amount as that ofthe carboxy group of the amide acid used. Further, a component (b)different from the component (b) was added (or no component was added)as shown in Table 5, followed by stirring, whereby photosensitive resinsolutions were obtained.

TABLE 5 Components (a)(c) Component (b) Comparative Example 1 Polymersolution I DAPM None Comparative Example 2 Polymer solution I DAPM B5Comparative Example 3 Polymer solution III DAPM B5 Comparative Example 4Polymer solution V DAPM B5 Comparative Example 5 Polymer solution VIIDAPM B5 B5 2 parts by mass ofbis(cyclopentadienyl)bis(2,6-difluoro-3(1H-pir-yl)phenyl) titanium and0.5 part by mass of diethylamino-3-thenoylcumarin were used incombination.

An evaluation was made in the same manner as in Examples. The resultsare shown in Tables 6 and 7.

TABLE 6 Thermal Hygroscopic expansion expansion Sensitivity Resolutioncoefficient coefficient mJ · cm⁻² μm ppm · K⁻¹ ppm⁻¹ Comparative Nopattern was obtained. 16 15 Example 1 Comparative 1000 30 18 19 Example2 Comparative 600 15 12 18 Example 3 Comparative 1000 30 12 20 Example 4Comparative 500 15 35 44 Example 5

As shown in Table 6, when a component different from the component (b)was used, a sufficient sensitivity could not be obtained. In particular,in Comparative Examples 2 and 4 in which the polymer has afluorine-substituted benzidine skeleton shown by the formula (4), theresidual film ratio (film thickness of an exposed part afterdevelopment/film thickness of an exposed part before development) wassignificantly low when a component different from the component (b) wasused. Specifically, although a pattern was obtained when exposure wasconducted at 1000 mJ/cm² or more, the residual film ratio was 30 to 60,which was too low to be put into practice.

In Comparative Examples 2 and 4, the hygroscopic expansion coefficientof the cured film was larger than that in Comparative Examples 1 and 3,which was not suitable for use in an interlayer insulating film or aprotective film of a suspension for a hard disc drive.

TABLE 7 arping of stainless plate mm Comparative Example 1  4Comparative Example 5 15 (plate was rounded, and no accurate measurementcould be conducted)

As shown in Table 7, the stainless plates of Comparative Examples 1 and5 underwent significant warping as compared with those of Examples.

Although some exemplary embodiments and/or examples of this inventionhave been described in detail above, those skilled in the art willreadily appreciate that many modifications are possible in the exemplaryembodiments and/or examples without materially departing from the novelteachings and advantages of this invention. Accordingly, all suchmodifications are intended to be included within the scope of thisinvention.

The documents described in the specification are incorporated herein byreference in its entirely.

1. A photosensitive resin composition for an interlayer insulating filmor a protective film of a substrate for circuit formation, wherein thephotosensitive resin composition comprises: a polymer (a) having astructural unit shown by the formula (A),

wherein R¹ is a trivalent or tetravalent organic group, R² is astructure shown by the following formulas (2) or (3),

wherein a plurality of R⁴s are independently a fluorine atom or amonovalent organic group having 1 to 10 carbon atoms that may have anoxygen atom, a sulfur atom or a halogen atom, and m and n areindependently an integer of 0 to 4, R is a monovalent organic grouphaving a carbon-carbon unsaturated double bond or a group shown by O⁻M⁺,in which M⁺ is a hydrogen ion or an ion of a compound having acarbon-carbon unsaturated double bond, and at least one of Rs is amonovalent organic group having a carbon-carbon unsaturated double bondor a group shown by O⁻M⁺, in which M⁺ is an ion of a compound having acarbon-carbon unsaturated double bond, and n is 1 or 2; and a compound(b) that generates a radical when irradiated with active rays and thathas a structure shown by the following formula (B),

wherein R³ is a monovalent aromatic or heterocyclic ring that may have asubstituent.
 2. (canceled)
 3. (canceled)
 4. The photosensitive resincomposition according to claim 1, wherein, in the structural unit shownby the formula (A), R² is a structure shown by the following formula(4),

wherein R⁵s are independently a fluorine atom or a trifluoromethylgroup.
 5. The photosensitive resin composition according to claim 1,wherein the compound (b) is a compound containing an oxime esterstructure.
 6. The photosensitive resin composition according to claim 5,wherein the compound (b) is shown by the following formula (5),

wherein R¹⁰ to R¹⁶ are independently a monovalent group.
 7. Thephotosensitive resin composition according to claim 6, wherein thecompound (b) is shown by the following compound (6),


8. The photosensitive resin composition according to claim 1, whereinthe compound (b) is contained in an amount of 0.1 to 20 parts by massrelative to 100 parts by mass of the polymer (a).
 9. The photosensitiveresin composition according to claim 1, wherein the substrate forcircuit formation is a supporting substrate of a suspension for a harddisk drive.
 10. A method for forming a pattern comprising the steps of:applying the photosensitive resin composition according to claim 1 to asubstrate for circuit formation, followed by drying to form aphotosensitive resin film; exposing the photosensitive resin film tolight; developing the photosensitive resin film after the exposure; andheating the photosensitive resin film after the development.
 11. Acircuit formation substrate that comprises, as an interlayer insulatingfilm or as a protective film, a layer with a pattern obtainable by themethod for forming a pattern according to claim
 10. 12. A circuitformation substrate that comprises a supporting substrate, an interlayerinsulating film, a conductor film and a protective film in a sequentialorder, wherein at least one of the interlayer insulating film and theprotective film is formed of the photosensitive resin compositionaccording to claim
 1. 13. The circuit formation substrate according toclaim 11, wherein the circuit formation substrate is a suspension for ahard disc drive.
 14. The photosensitive resin composition according toclaim 1, wherein R in the formula (A) is a monovalent organic grouphaving a carbon-carbon unsaturated double bond.
 15. The photosensitiveresin composition according to claim 1, wherein R in the formula (A) isa monovalent organic group having a carbon-carbon unsaturated doublebond.